Brazing Tips
1. Proper Joint Clearances
During the brazing process, 2
closely fitted surfaces or base metals are heated and a filler metal is
introduced. As the filler metal becomes molten it is drawn into
the joint by capillary action. The joint strength is a function of
the joint design. The joint must have the proper amount of
clearance between the base metals. See the table below for recommended
clearance at the brazing temperature. Remember that the metals
will expand when heated.
Recommended Joint Clearances at brazing
Temperatures
2. Pre-cleaning of Base Metals
The metals to be
joined must be cleaned prior to brazing. Cleaning can be accomplished
by chemical or mechanical means. Chemical cleaning can be done by
vapor degreasing, chlorinated solvents, acid pickling cleaning or Fuze-Clean
cleaning products. Mechanical cleaning can be done by grinding,
machining, sandblasting or wire brushing.
3. Proper
Fluxing of the Base Metals
Fluxing and atmosphere brazing are used
to stop/prevent the formation of oxides on the base metals during the
heating process. Oxidation limits capillary action and decreases
joint strength. Copper Filler metals containing Phosphorus act as
a fluxing agent to prevent oxidation. In many case an additional
flux is not required.
4. Brazing
This is where the heat
is introduced to the assembly. There are several basic heating
methods; torch, resistance, induction, vacuum and atmosphere
furnaces. Torch heating can be done with any fuel such as oxy-acetylene.
The filler metal will tend to flow toward the heat. Do not
directly heat the filler metal, this can lead to a very low strength
joint. Heat must be applied uniformly to both parts to be
joined.
Induction and resistance heating can be cost effective
for medium volume production.
Furnace heating is usually used for
higher production volumes and difficult to join
materials.
5. Post Cleaning
After
brazing, the flux residue must be removed because they are
corrosive. The most common was is to water quench the assembly
into a hot water bath. This will normally break up the flux
residue. The residue can also be removed by mechanical
means. For hard to remove and residue with blackish color our Fuze-Clean
FS works very well.
